Scanning electron microscopic observations of endothelial changes in experimentally induced atheromatosis of rabbit aortas.

Following the administration of cholesterol for a period of 6-7 weeks, Scanning Electron Microscopic (S.E.M.) observations revealed mono-cellular, crater-like and dome-shaped endothelial changes on top of the large intimal plaques in the rabbit aortas. Finger-like and other shaped cell protrusions were observed at the edges of these crater-like and dome-shaped endothelial changes, giving the intimal plaques a rough appearance. At other sites, normal, smooth, although irregularly arranged, endothelial cells covered the lesions. By impregnating the cell borders with silver-nitrate or silver proteinate containing perfusates, it was possible in most cases to ascertain that the lesions were derived from changes in one cell or from changes in a small collection of cells. S.E.M.-observations further revealed crater-like and dome-shaped endothelial changes to be present in large fields or as isolated cell changes in normal areas at sites where no gross lesions were observed with the light microscope. In addition large, multi-cellular, crate-like endothelial changes were observed at the edges of the large intimal plaques. At these sites several endothelial cells were lacking, leaving behind a crater in which sometimes cells and a few fibrin threads were found. Following the administration of cholesterol for periods of 4-5 and 2-3 weeks similar monocellular changes were observed, some extending over large areas, other as single cells in apparently normal surroundings. Quantitatively the number of lesions was less than when the cholesterol was administered for a longer period. Transmission electron microscopic studies revealed the presence of large amounts of membrane-bound lipid globules in the subendothelial spaces and within some endothelial cells, structures which were assumed to be cross-sections of the crater-like or dome-shaped endothelial cell protrusions, visible with the S.E.M.